nx_fnptr_slot_probe.nx

nx_fnptr_slot_probe.nx -- DECISIVE probe: does a struct with MORE THAN ONE function-pointer field dispatch to the right slot? The arity probe showed every struct-field fn-ptr call returning garbage while the same callees invoked directly (or through a let-copied local) return the right answer. Two hypotheses survive: H1 the indirect call-site mangles ARGUMENTS (arity/register related), or H2 the FIELD OFFSETS of fn-ptr-typed struct members collapse, so every vtable slot aliases and a call lands in whichever function was assigned last. H2 would be far more serious: it silently breaks every multi-method vtable in the tree. This probe discriminates them with ZERO argument passing. Five nullary functions, each returning a unique constant, stored in five separate fields. If each slot returns its own constant, offsets are fine and the fault is in argument passing. If they all return the SAME constant, the fields alias. license_tier: ORIGINAL